Method for controlling well blowouts

ABSTRACT

Uncontrolled flow of oil and gas from petroleum wells located in a body of water, is stopped by a procedure performed below the water surface at a location which is free from wave action and is safe from the danger of fire or explosion. An access conduit line is hot-tapped into the production tubing through access windows formed in the well casing. The production tubing is then crimped above the hot tap and solid particles are then introduced into the production tubing through the access line where they are carried upwardly by the flowing well fluids to lodge within the restriction and form a plug. Heavy, noncombustible &#39;&#39;&#39;&#39;mud&#39;&#39;&#39;&#39; is then pumped into the tubing through the access line until the weight of the injected mud overcomes the formation pressure, thus terminating well flow. Where the well is located on land, the method of the present invention may be practiced by obtaining access t the well structure at the point below the land surface for formation of the hot tap and crimp.

United States Patent Rowley et al.

[ Mar. 7, 1972 [54] METHOD FOR CONTROLLING WELL BLOWOUTS [72] Inventors: Kermit G. Rowley, Houston, Tex.; Richard H. Barron, Lafayette, La.

[73] Assignee: Tenneco Oil Company, Houston, Tex.

[22] Filed: Apr. 16, 1970 [21] Appl. No.: 29,091

[52] US. CL ..l66/285, 137/15, 137/318, 166/.5, 166/297 [51] Int. Cl. ..E21b 33/035, E211) 35/00 [58] Field ofSearch ..l66/.5,.6, 284, 285,55,55.1, 166/90; 137/247, 247.11, 315-318, 15, 13; 175/226, 233; 251/1, 4; 61/1 F [56] References Cited UNITED STATES PATENTS 1,563,520 12/1925 Owen ..166/285 3,028,914 4/1962 Flickinger 1 66/284 3,144,049 8/ 1964 Ginsburgh..... .166/284 X 2,000,381 5/1935 Duffy ..166/90 2,840,166 6/1958 Eckel et al. 166/55 3,277,964 10/1966 Houpeurt et a1 ..166/285 Primary Examiner-Stephen .I. Novosad Attorney-Eugene S. Coddou [57] ABSTRACT Uncontrolled flow of oil and gas from petroleum wells located in a body of water, is stopped by a procedure performed below the water surface at a location which is free from wave action and is safe from the danger of fire or explosion. An access conduit line is hot-tapped into the production tubing through access windows formed in the well casing. The production tubing is then crimped above the hot tap and solid particles are then introduced into the production tubing through the access line where they are carried upwardly by the flowing well fluids to lodge within the restriction and form a plug. Heavy, noncombustible mud is then pumped into the tubing through the access line until the weight of the injected mud overcomes the formation pressure, thus terminating well flow.

Where the well is located on land, the method of the present invention may be practiced by obtaining access t the well structure at the point below the land surface for formation of the hot tap and crimp.

14 Claims, 7 Drawing Figures PATENTEU 7 I97? CMRMJ H UULOJ ATTORNEY METHOD FOR CONTROLLING WELL BLOWOUTS BACKGROUND-OF THE INVENTION 1. Field of the Invention The present invention relates to means for controlling the flow of liquids and gases through a well conduit. :In particular, the present method relates to means :for stopping the uncontrolled flow of petroleum fluidsthrough apro'duction tubing string in a well. As used herein, the term fluids is intended to encompass both liquids and gases.

2. Brief Description of the Prior Art It is well known that petroleum fluids in subterranean formations are often under relatively high pressures and when such formation are penetrated by awell, the pressurized formation fluids tend to flow naturally to the surface through the well conduits. Control equipment such as valves rand chokes are included at the wellhead for'the purpose of confining or regulating the flow of the pressurizedpetroleum'fluids.

When for any reason, the control equipmentforlthe well-is damaged, destroyed or rendered inoperative, the pressurized fluids in the formation may flow uncontrollably'through the well conduits toward the surface resulting in what iscommonly referred to as .a blowout." Often, automatic valves called storm chokes which areregulated by'the rate of fluid flow through the valve are positioned within the well conduits for the purpose of automatically closing-'orstopping the well flow when it exceeds a predetermined value. While storm chokes and other safety devices of similar type are suitable for performing their intended safety function when operating properly, it has been found that well 'flow through such chokes causes abrasion of the choke closure means and may also deposit silt and sand within the moving components of the choke thereby rendering the choke inoperative. For :this reason, the storm chokes must be periodically inspectedzand replaced.

Often when uncontrolled well flow occurs,the combustible fluids leaving the wellhead are ignited 'thuspreventing'capping efforts at the near vicinity of the wellhead until the flames have been extinguished. Where the well is located in a body of water, the escaping well fluids are often intentionally setafire to prevent water pollution and to limit the damage to vegetation, vessels, and structures caused by oil floating on the water's surface.

One of the primary prior art techniques employed 'to stop uncontrolled well flow requires that the wellhead first be blown off with explosives. The blaze is then extinguishedrand the well may then be capped with a specially designed valve arrangement. This prior art process is hazardous and time consuming and also permits the well effluents to flow onto and pollute the surrounding water area. Even after the combustion is stopped, the capping operation remains extremely dangerous in that the highly combustible effluents may ignite at any time. In water locations, heavy wave action may also severely limit capping operations and can also appreciably increase the danger of the operation.

Another prior art method suggested for extinguishing the uncontrolled flow of fluid in wells is described in U.S.Pat. No. l,879,l60 which issued Sept. 27, 1932 to F. B. Fowzer. In the patented process, the inventor proposes tunneling below the earths surface to obtain access to the well conduit below the escaping fluids. Once the tunnel had been completed, a tap was made through the well casing and hardenable fluid such as cement was pumped into the annular area'betweenthe casing and the internal well conduits to form a solid annular plug. Thereafter, the cement was chipped away and a second tap was made into the next internal well conduit. A specially constructed plug was then pumped into the second tap to form a seal between the internal well conduit and a smaller drilling line conduit contained within the internal conduit. After having formed the requisite seal, a heavy noncombustible fluid was then pumped through the second tap with the specially constructed plug acting to direct the fluid downwardly through the annular area between the internal well conduit and'the 'drilling'lineconduit. The mud flow was thus'U-tubed"'intothe'end of the drilling line conduit to stop the flow of petroleum fluids 'to the wellhead, extinguishing the surface 'fire.=Presumably, mud was then-continually pumped into the second tap and up through the drilling line conduit until the latter conduit could bercapped.

it will be appreciated that the need -for a specially constructed .plug of the type required in the Fow'zer teaching ."places seriouslimitations upon the versatility ofthe suggested 'procedurezand also increases the danger-of malfunctiomln adproposed in which a number of flow control and fireextin- 'guishing devices could be contained. A side access tunnel lead from'thesurface tothe cage. The Duffy proposal also included a piercing means whereby-the well casing and production tubing string could be pierced so that fire-quenching steam or other fluid or gas could be supplied to the petroleum conducting conduit.

More recently in 1966, US. Pat. No. 3,277,964 issued to Houpeurt .et al. for a method for controlling the discharge of combustible fluid from oil wells and the like. The Houpeurt teaching discloses a process for controlling high-pressure effluent discharge from oil wells by'tapping into two vertically .spaced subterranean points of the well with two branch conduits, forming a crimp in the production tubing between the two branch conduits with the lower branch being open to divert the effluent flow and reduce the'pressure in the production tubing, pumping a plugging material into the tubing through the upper branch and when the plug is formed, injecting a heavy mud into the tubing through the'lower branch line.

SUMMARY 'OF THEIINVENTION The method of the present invention affords a rapid, economical, and simple procedure wherein the uncontrolled flow of an oil or gas well may be stopped without endangering men and equipment. Moreover, the method of the present invention may be practiced while the escaping well effluents are .burning at the wellhead thus preventing water pollution caused :by .the-uncontrolledflow of the liquids onto the water surface. While the .primary emphasis of the present invention is directedtoapplications in water environments, it will be appreciated that the steps of the method may be applied to land 'wellstoachieve the same beneficial results.

In its broad aspects, the present invention encompasses the introduction of plugging bodies into a fluid conduit at a point upstream from a flow restriction contained in the conduit whereby theplugging bodies move to the restriction and form aplug which substantially or totally stops flow through the conduit.

in specific application, the process of the present invention contemplates the formation of access openings or windows in the protective casing strings of a well at a protected point below the well surface. In water environments, such windows may be formed'by divers, operating'below the surface of the water and above the bottom of the water area. In this protected zone, men and equipment are free from the intense heat generatedby the'burning effluents and may work in relative safety. A hot tap is made into the flowing production tubing through the casing windowJThe term"hot tap as employed herein refers to the connection of a fluid-carrying access line' into the flowing well conduit while the well conduit remainsunder pressure, without any substantial fluid leakage or pressureloss fromthe flowing well conduit during the formation of the connection. Such hot taps may be'formed with conventional equipment which is readily available and well known in the art.

Once the hot tap has been made, the production tubing is partially squeezed together above the point of the hot tap. Thereafter, solid materials are inserted into the production tubing through the access line. The flow of well effluents through the production tubing carries the inserted solid materials upwardly to the squeezed area where they become lodged. As the solid particles accumulate they eventually form a plug, first further restricting and thereafter substantially shutting off flow of the petroleum fluids through the production tubing. Once flow of the well fluids has been sufficiently reduced, a well control material such as a heavy, noncom bustible fluid or mud" is inserted into the production tubing through the access line to create a back pressure against the formation. When sufficient mud has been introduced into the production tubing, the weight of the mud forms a back pressure which overcomes the formation pressure thereby terminating the natural flow of petroleum fluids toward the surface. When the well flow has been thus terminated, the access line may be closed and the well may be temporarily or permanently abandoned or reworked.

The method of the present invention is thus seen to be efficient, quick and reliable, while also affording increased safety to men and equipment in that danger from fire, explosion and rough water surface conditions are virtually eliminated.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation, partially broken away, of an exemplary well installation employed in wells located in water;

FIG. 2 is a partial elevation, partially broken away, illustrating a portion of the well structure of FIG. 1 having windows cut through protective casing to expose the production tubing string of the well;

FIG. 3 illustrates a hot tap device connected to the production tubing string of the well assembly illustrated in FIGS. 1 and 2 with the remaining well components omitted for purposes of clarity;

FIG. 4 illustrates the production tubing string and hot tap of FIG. 3 in vertical section;

FIG. 5 is a view similar to FIG. 4 illustrating the formation of a crimp in the production tubing string above the hot tap apparatus.

FIG. 6 is a view similar to FIG. 5 illustrating the insertion of solid particles into the tubing string through the hot tap; and

FIG. 7 is a view similar to FIGS. 5 and 6 illustrating a bridge or plug formed within the production tubing string by the solid particles.

DESCRIPTION OF THE PREFERRED EMBODIMENT As previously indicated, the method of the present invention is primarily directed to use with wells located in water. It will be understood however, that the basic steps of the present invention may be employed with wells located on land. As used herein, the term blowout" is meant to represent the uncontrolled flow of well fluids from a well; the term fluids" is intended to encompass both liquids and gases; the term hot tap" is intended to define the connection of a fluid-conducting conduit to a second conduit without the need for decreasing the pressure of the contents of the second'conduit and without any substantial pressure loss or loss of the contents of the second conduit through the point of connection with the first conduit; the term production tubing string as used herein is intended to include any conduit in the well structure which contains petroleum fluids underpressure which, under conditions of a blowout, are uncontrollably escaping from some point along the vertical development of the conduit.

Referring to FIG. I of the drawings, a typical well structure indicated generally at S is illustrated within a body of water indicated generally at W. The well structure S extends above the top of the surface of the water W and normally terminates at'a well head (not shown) which includes regulating and control equipment and fittings for conducting the well fluids to a collection point.

The structure S includes an external conductor pipe 10 which extends from above the surface of the water W to a point somewhat below the surface of the water bed indicated generally at B. An intermediate casing string 11 and a producing casing string 12 are carried concentrically within the conductor pipe 10 and extend to different subterranean points within the well bore. Concrete 13 is illustrated within the annular space between the conductor pipe 10 and intermediate casing string 11. A production tubing string 14 extends through the center of the well structure S and is nonnally the principle conductor employed for conveying the petroleum fluids from the subterranean formation to the wellhead.

Under normal conditions, with a well structure such as illus trated in FIG. 1, petroleum fluids in the formation are conducted through the production tubing string 14 during a blowout. The intermediate and production casing strings normally contain little or no pressure and effluent flow is limited to the production tubing string 14. While the method of the present invention is described herein in detail with respect to the exemplary structure illustrated in FIG. 1, it will be appreciated that the method may also be employed in many other structures.

In the method of the present invention, upon occurrence of a blowout, divers enter the water W and obtain access to an area indicated at C along the structure S. The vertical location of the area C is sufficiently below the water surface to protect the divers and equipment employed by the divers from the heat generated by fluids burning at the wellhead or if not burning, to protect the divers and equipment from the danger of subsequent fire or explosion upon accidental ignition of such fluids. Where the distance between the water bed B and the water surface is sufficiently great to provide the required overhead protection to men and equipment, the area C is located above the water bed B. Where insufficient clearance exists between the water bed B and the water surface, the required vertical spacing below the point of escape of the well fluids is acquired by any suitable means including tunneling through the bed B or clearing an area around the well structure S by removing portions of the bed. In most wells located in bodies of water in the ocean or in waters such as the Gulf of Mexico, the vertical distance between the water surface and the bed B provides ample working room and overhead protection. In some inland waters or other locations where water depth may be relatively shallow, the tunneling or clearing type procedure previously referred to may be employed.

Referring to FIG. 2, once access to the desired area C of the well structure has been obtained, openings or windows 10a, 13a, 11a, and 12a are formed in the conductor pipe 10, concrete layer 13, intermediate casing 11, and production casing 12 respectively. The windows formed in the well structure S provide access to the production tubing string 14 which, as previously indicated, conducts the uncontrollably flowing well fluids during a blowout. The size of the access windows formed in the structure S is dependent upon the equipment employed to complete the hot tap and crimping steps of the present invention. It will be understood that while ample working room is desirable, the size of the access windows should not be so large as to present the risk of weakening the structure S and permitting it to bend or fall over. If desired, an additional window or windows may be formed at vertically spaced points along the structure S to provide different access points for the crimping and hot tap operations.

The access windows through the well structure S may be formed by various conventional techniques including underwater cutting torches, mechanical cutters, and shaped charges. It will be appreciated that during the formation of the access windows in the well structure, care must be exercised in cutting into high-pressure areas within the well structure. Where such high-pressure areas are the result of static fluid columns and are not induced by the'formation pressure, the

pressure may be bled off in any conventional manner before the access windows are cut through the protective structure surrounding the producing tubing 14.

When the production tubing string 14 has been sufficiently exposed, a hot tap indicated generally at H in FIG. 3 is made into the tubing string. The hot tap H is conventional and may include a half-sleeve 15 which mates with a second half sleeve 16. A lateral access conducting line 17 extends from the halfsleeve 16 and includes a valving mechanism V which may be employed to open and close flow through the access line 17. The hot tap sleeve sections 15 and 16 are positioned around the production tubing string 14 and secured to the tubing string by any suitable means such as clamps 19 and '20. The vertically extending seams between the two sleeve sections 15 and 16 include suitable packing (not illustrated) to prevent leakage and packing 21 and 22 illustrated in FIG. 4 is positioned between the hot tap H and the tubing string 14 to prevent leakage through the top and bottom of the mating sleeves l5 and 16. With the hot tap H thus clamped into position about the tubing string 14, the valve V isopened and, a suitable boring apparatus is inserted through the line 17 and the valve V to cut through the wall of the tubing string 14. The boring apparatus (not illustrated) normally includes a suitable packing gland or other means whereby the cutting component entering through the access line 17 may be withdrawn from the line 17 and the valve V without any substantial lossof pressure or fluid. With the cutting mechanism extracted from the line 17 in valve V, the valve V may be closed to prevent any pressure loss or flow through the line 17.

From the foregoing, it will be understood that the hot tap H pennits the access line 17 to be attached to the production tubing 14 with a leakproof, pressuretight flow-conducting connection being formed between the access line and the production tubing. Thus, a connection such as illustrated in FIG. 4 is permitted even though the internal contents of the tubing string 14 are rapidly flowing and are under relatively high pressures. The valve V in line 17 is immediately closed after the tapping or cutting device is extracted from the line 17 to prevent any flow of the contents of the production string 14 into the access line 17.

Once the hot tap connection has been completed, a restriction to effluent flow is formed in the production tubing string at a point which is down stream from the hot tap connection. It will be understood that in the event a suitable restriction already exists above the hot tap level, formed for example by a partially opened valve or other control equipment, noladditional restriction is required. With reference to FIG. 5, a preferred restriction indicated generally at R is formed by squeezing or crimping the production string 14 to restrict its internal flow passage. In its simplest form, the restriction R may be formed by squeezing the string 14 between two opposed jaws in a suitable squeeze device (not illustrated). It will also be appreciated that a restriction to effluent flow to the production tubing string 14 may be formed in a variety of specific shapes with a variety of techniques or equipment.

Following the formation of the restriction R, plugging bodies P are introduced into the production string 14 through the access line 17. These plugging bodies are carried from the point of entry at the access line 17 toward the restriction by the flow of petroleum effluents through the production tubing string. As illustrated in FIG. 6, the size of the bodies P, is preferably larger than the internal dimensions in the restricted area of the production string whereby the bodies are lodged or prevented from flowing through the restriction. The bodies P, accumulating at the restriction R form a partial plug which further restricts the flow of well effluents through the restricted area. If required, successively smaller particles indicated at P and P may be sequentially introduced into the tubing string 14 with the larger particles being introduced first to form a plug indicated generally at P in FIG. 7.

When the plug P has terminated or substantially terminated, flow of petroleum fluids through the production string 14, a suitable, noncombustible high-density well control material or mud is then introduced into the tubing string through the access line 17 at a pressure which is sufficient to overcome the formation pressure and displace the petroleum fluids from the production string 14. The mud flowing in the direction of the arrow 23 is inserted into the production string 14 until the weight of the inserted mud is sufiicient to overcome the formation pressure. Thereafter, the valve V in the line 17 may be closed and the'well may be abandoned or repaired as desired.

In its broad terms, it will be appreciated that the method of the present invention encompasses the steps of inserting plugging materials into a conduit at a point which is upstream from a restriction in the conduit causinga plug to form internally of the conduit in the area of the restriction to thereby terminate or substantially terminate the flow past the restriction or plug. The particular apparatus employed in forming the restriction or in forming the upstream access point for introduction of plugging materials is conventional and,-while improved equipment and techniques for effecting these steps is vanticipated and may form the-subject matter of future patent applications, such apparatus and technique form no part of the present invention.

It will be understood that any suitable means may be employed for supplyingtheplugging bodies and mud to the access'line 17. Thus, by way of example, the access line 17 may extend'to a vessel located at the waters surface which may pump the plugging bodies and mud through the line 17. If desired, however, suitable subsurface equipment may be employed for the same purpose.

The plugging bodies P, are preferably although not necessarily less dense than the petroleum effluents. It will be understood, however, that the method of the present invention is readily capable of use with plugging materials of any density provided only that the bodies must be able to move from the point of insertion to the restricted area. Thus, where the point of insertion is vertically below the restricted area, the flow of effluents must be strong enough to elevate the plugging bodies to the restricted area. lt will be understood, however, that even where the effluent is primarily gas, high-pressure gaseous flow may be sufficient to elevate even steel balls into sealing engagement with a restriction. Where the effluent is oil, or other liquid, it is desirable although not necessary that the plugging bodies be buoyant in the liquid to prevent any tendency of the plugging material to settle in the effluent once flow through the tubing string has been terminated. It should be emphasized, however, that even where the plugging materials are of greater density and are not buoyant in the well effluent, the plug will normally remain lodged in position.

It is also noted that while reference has been made to the use of divers for underwater work associated with the method of the present invention, other means may be employed. Thus, a watertight capsule or other suitable means might be secured around the structure S permitting men to work without diving equipment.

The foregoing disclosure and description of the invention is illustrative and explanatory thereof, and various changes in the procedures as well as in the details of the described method may be made within the scope of the appended claims without departing from the spirit of the invention.

What is claimed is:

l. A method for controlling the flow of effluents such as oil and/or gas under pressure through a conduit comprising the steps of:

a. inserting plugging materials into said conduit at an inserting point upstream from a flow restriction in said conduit;

b. moving said plugging materials to said flow restriction to form a plug within said conduit which reduces or which completely terminates effluent flow through said conduit; and

c. inserting a noncombustible, relatively heavy liquid well control material into said conduit at said inserting point after the formation of said plug.

2. The method as defined in claim 1 wherein said effluents are partially or completely displaced from said conduit by said well control material, and said well control material is inserted into said conduit until the pressure created by the weight of said well control material is greater than or substantially equal to the pressure of said effluents.

3. The method as defined in claim 2 further including the step of forming an opening into said conduit at said inserting oint. p 4. The method as defined in claim 3 further including the step of forming a restriction to effluent flow through said conduit at a point which is downstream from the inserting point.

5. The method as defined in claim 4 wherein said opening at said inserting point is formed with a hot tap.

6. The method as defined in claim 5 wherein said restriction to efi'luent flow is formed by deforming the walls of said conduit.

7. The method as defined in claim 6 wherein said plugging materials include a plurality of small plugging bodies having external dimensions which are large enough to prevent passage through said restriction.

8. The method as defined in claim 7 wherein said plugging bodies are graded in size and the larger of said plugging bodies are inserted into said conduit first.

9. The method as defined in claim 8 wherein said conduit is part of an oil and/or gas well structure and including the initial step of removing portions of said well structure surrounding said conduit to expose said conduit.

10. A method for controlling the flow of petroleum effluents through a production tubing string in an oil or gas well following a blowout of said well comprising the steps of:

a. obtaining access to the well structure at least one work point spaced vertically below the point where the well effluents are escaping;

b. forming access openings through any well structures surrounding the production tubing string at said work point;

e. connecting an access conductor line into the production tubing string at the work point;

d. forming an initial restriction in the production tubing string at a point spaced vertically above the connection of the access line into the tubing string to form an initial restriction to the flow of petroleum effluents through the tubing string; and

e. inserting plugging material into the tubing string through said access line whereby said plugging materials lodge 'in the restricted tubing string to form a plug which restricts or terminates effluent flow through the tubing.

11. The method as defined in claim 10 including the further step of inserting a liquid into said tubing string through said access line following formation of said plug to decrease the pressure within-the tubing string at the work point.

12. The method as defined in claim 10 wherein said plugging material introduced into said tubing string includes solids in the form of a plurality of separable bodies having dimensions and physical characteristics suitable for forming and maintaining said plug.

13. The method as defined in claim 12 wherein said bodies having the largest external dimensions are introduced into the tubing string first.

14. The method as defined in claim 10 wherein said initial restriction is formed by deforming said production tubing string. 

1. A method for controlling the flow of effluents such as oil and/or gas under pressure through a conduit comprising the steps of: a. inserting plugging materials into said conduit at an inserting point upstream from a flow restriction in said conduit; b. moving said plugging materials to said flow restriction to form a plug within said conduit which reduces or which completely terminates effluent flow through said conduit; and c. inserting a noncombustible, relatively heavy liquid well control material into said conduit at said inserting point after the formation of said plug.
 2. The method as defined in claim 1 wherein said effluents are partially or completely displaced from said conduit by said well control material, and said well control material is inserted into said conduit until the pressure created by the weight of said well control material is greater than or substantially equal to the pressure of said effluents.
 3. The method as defined in claim 2 further including the step of forming an opening into said conduit at said inserting point.
 4. The method as defined in claim 3 further including the step of forming a restriction to effluent flow through said conduit at a point which is downstream from the inserting point.
 5. The method as defined in claim 4 wherein said opening at said inserting point is formed with a hot tap.
 6. The method as defined in claim 5 wherein said restriction to effluent flow is formed by deforming the walls of said conduit.
 7. The method as defined in claim 6 wherein said plugging materials include a plurality of small plugging bodies having external dimensions which are large enough to prevent passage through said restriction.
 8. The method as defined in claim 7 wherein said plugging bodies are graded in size and the larger of said plugging bodies are inserted into said conduit first.
 9. The method as defined in claim 8 wherein said conduit is part of an oil and/or gas well structure and including the initial step of removing portions of said well structure surrounding said conduit to expose said conduit.
 10. A method for controlling the flow of petroleum effluents through a production tubing string in an oil or gas well following a blowout of said well comprising the steps of: a. obtaining access to the well structure at least one work point spaced vertically below the point where the well effluents are escaping; b. forming access openings through any well structures surrounding the production tubing string at said work point; c. connecting an access conductor line into the production tubing string at the work point; d. forming an initial restriction in the production tubing string at a point spaced vertically above the connection of the access line into the tubing string to form an initial restriction to the flow of petroleum effluents through the tubing string; and e. inserting plugging material into the tubing string through said access line whereby said plugging materials lodge in the restricted tubing string to form a plug which restricts or terminates effluent flow through the tubing.
 11. The method as defined in claim 10 including the further step of inserting a liquid into said tubing string through said access line following formation of said plug to decrease the pressure within the tubing string at the work point.
 12. The method as defined in claim 10 wherein said plugging material introduced into said tubing string includes solids in the form of a plurality of separable bodies having dimensions and physical characteristics suitable for forming and maintaining said plug.
 13. The method as defined in claim 12 wherein said bodies having the largest external dimensions are introduced into the tubing string first.
 14. The method as defined in claim 10 wherein said initial restriction is formed by deforming said production tubing string. 